Electromagnetic Simulations of VMTSA Equipped with the

RF Fingers and Ferrites

O. KononenkoCERN, BE/RF

JINR

Thanks to Benoit Salvant, Alexej Grudiev, Elias Métral

LRFF Meeting, CERN, October 30, 2012

2

Outline

• Realistic finger deformations for VMTSA equipped with the longer fingers. Time domain, eigen frequency and wire simulations

• Simulations of the deformed shorter fingers and effect of Philips 8C11 ferrites

3

RF Fingers Deformation in VMTSA

4

Simulated VMTSA models

Conforming fingers

Wire,conforming fingers

Wire,no fingers Bad contact

2st type

Deformation+Ferrites

Wire,20-50mm gaps

Completed In progress

Old longer fingers New shorter fingersConforming and bad contactfingers

Bad contact 1st type

5

VMTSA with Wire and Comforming Fingers

Port 1

Port 2

Copper

Perfect H Model:

- 180 deg of the structure- copper outer walls

Simulation profile: - second order basis functions

- curvilinear elements enabled- discrete sweep from 20MHz to 2GHz, 20MHz step- 0.01 s-parameters accuracy => ~220K tet10 mesh

Wire

- no matching

6

VMTSA with Wire and Deformed Fingers: 20-40mm gaps

Port 1

Port 2

Copper

Perfect H Model:

- 180 deg of the structure- copper outer walls

Simulation profile: - second order basis functions

- curvilinear elements enabled- discrete sweep from 20MHz to 2GHz, 20MHz step- 0.01 s-parameters accuracy => ~260K tet10 mesh

Wire

Gap: 20-40mm

Gap- no matching

7

VMTSA with Wire andMore Realistic Deformation

Port 1

Port 2

Stainless Steel

Perfect H Model:- 180 deg of the structure- copper outer walls

Simulation profile: - second order basis functions

- curvilinear elements enabled- discrete sweep from 10MHz to 2GHz, 10MHz step- 0.01 s-parameters accuracy => ~300K tet10 mesh

Wire

Gap: 40-50mm

Gap- no matching load

8

Transmition for Different Gap Sizes

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-35

-30

-25

-20

-15

-10

-5

0

Frequency, GHz

S 21, d

B

40 mm50 mm

Different level of transmission probably because there is no matching load in the HFSS simulation

9

CST TD Simulations of VMTSA Model:

- full structure- copper walls- conforming fingers and 40-50 mm gap

Simulation profile: - 10 lines per wavelength - refine at PEC by factor 6 - 70mm bunch sigma

- 400K hex mesh

10

Longitudinal Impedance

11

Longitudinal Wake Potential

12

Ht for Bunch Passage through VMTSA

13

Power Spectrum Measurements

HFSS Eigen Mode Analysis: 40mm

14

Mode Complex Magnitude

Eigen Frequency

[MHz]Q-factor

Shunt Impedance,

[Ω]Power Loss

[W]

1 279 455 10050.5 652.8

2 342 211 192.6 12.5

3 370 163 7.5 0.6

4 383 134 1.7 0.1

5 390 114 0.6 0.04

WV

QR zL

2

dVEEWV

*0

2

dzefzEVL

czizz

0

/),(

Longitudinal Shunt Impedance

Voltage along the beam path

Energy stored in the volume

15

HFSS Eigen Mode Analysis: 50mm

Mode Complex Magnitude

Eigen Frequency

[MHz]Q-factor

Shunt Impedance

[Ω]Power Loss

[W]

1 270 387 7121.6 462.6

2 330 145 50.2 3.3

3 362 147 7.2 0.6

4 380 127 8.4 0.7

5 392 115 3.1 0.2

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Surface Loss Density for the First Eigen Mode @ 279 MHz

Log scale, 40 mm gap, eigen mode @ 279MHz with 10KΩ longitudinal shunt impedance

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Shorter RF FingersHFSS Simulation Setup: Eigensolver

Perfect H

Copper

Simulation profile: - second order basis functions

- curvilinear elements enabled- 1% frequency accuracy leads to ~300K tet10 mesh

Model:- 180 deg of the structure- copper outer walls- 10mm gap

10 mm gap

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0.113 V/m

0.037 V/m

0.030 V/m

0.005 V/m

0.028 V/m

Shorter RF Fingers, CmplxMag(E)

Mode 1

Mode 2

Mode 3

Mode 4

Mode 5

Eigenmodes of the Bellows

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Eigen Frequency, MHz

Q-factor Shunt Impedance, Ω

Power Loss,W

HFSS CST HFSS CST HFSS CST HFSS CST

Mode 1 339 339 2409 32 50709 676 2616 87

Mode 2 526 531 1872 322 8442 1438 275 186

Mode 3 549 550 6023 6837 0 0.03 0 0.004

Mode 4 586 583 2462 155 196 7 5 0.907

Mode 5 670 - 1217 - 389 - 5 -

Eigen Modes, Shorter RF Fingers

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VMTSA equipped with Ferrites

4 pieces of Philips 8C11 (60x30x5 mm) were installed in one VMTSA module equipped with the shorter fingers

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Philips 8C11 Ferrite: Permeability

10-3 10-2 10-1 100100

101

102

103

Frequency, GHz

Perm

eabi

lity

http://www.ferroxcube.com/appl/info/HB2009.pdf

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Philips 8C11 Ferrite: Resistivity and Permittivity

10-3 10-2 10-1 100 101 10210

20

30

40

50

60

70

80

90

100

Frequency, MHzR

elat

ive

Perm

ittiv

ity

10-1 100 101 1020

1

2

3

4

5

6

7

8

9

10x 104

Frequency, MHz

Res

istiv

ity,

m

http://www.ferroxcube.com/appl/info/HB2009.pdf

23

HFSS Setup

Perfect H

Copper

Simulation profile: - second order basis functions

- curvilinear elements enabled- 1% frequency accuracy

Model:- 180 deg of the structure- copper outer walls- 10mm gap- 4 ferrite pieces

10 mm gap

Ferrite 8C11

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New Fingers Ferrites 10mm Mode Eigen Frequency

[MHz]Q-factor Shunt

Impedance [Ω]

Power Loss[W]

1 133 1 0.239 0.019544

2 133 1 0.007 0.000572

... ... ... ... ...

3 341 2479 52455 2706

... ... ... ... ...

4 528 1867 8401 316

... ... ... ... ...

Many modes excited in the vicinity of ferrites and in the area outside the conforming fingers. Some modes excited near to the gap and not affected by ferrites at all

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Eigenmodes, CmplxMag(E)

133 MHz

133 MHz

341 MHz

528 MHz

Mode 1

Mode 2

Mode 3

Mode 4

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Surface Loss Density for the First Eigen Mode @ 341 MHz

Linear scale, 10 mm gap, eigen mode @ 341MHz with 2700 W power losses

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Conclusions

• Different shapes of the finger deformations have been studied for longer and shorter fingers. Unconformities could result in ~kW power losses => enough to melt fingers.

• Ferrites in the proposed position and amount don’t help. Additional dedicated study is necessary to see if we can damp modes with ferrites.